1. Field of the Invention
The invention relates to asphalt compositions and to a process for the improvement of their properties. The invention further relates to modified asphalt compositions useful in a variety of applications, particularly paving asphalts.
2. Description of the Prior Art
In the production of asphalt, crude oil is fractionated in a crude tower to produce crude tower bottoms which are passed to a vacuum tower to produce vacuum tower bottoms which can be sent directly to asphalt product. In addition, the asphalt product can be varied by adjusting conditions in the vacuum tower. For example, the asphalt can be made to have a higher viscosity by operating the vacuum tower at a higher temperature and/or lower pressure to remove heavier distillate as overhead from the vacuum tower. Alternatively, the asphalt can be increased in viscosity by oxidizing it. While this suffices for most 1980 or earlier asphalt specifications, it is difficult to meet newer specifications by merely altering the temperature and pressure of the vaccum tower, or even by oxidation. Indeed, recent asphalt specifications may preclude oxidation of the asphalt. In such instances, the methods of varying the properties of the finished asphalt to meet desired specifications will be to adjust conditions in the vacuum tower, to actually purchase crudes suited for producing the particular asphalt product desired, to add relatively expensive polymer additives to the asphalt and/or to add a mixture of solvent deasphalting bottoms and aromatic extract.
Solvent deasphalting (extraction of asphalts from heavy petroleum stocks) is a well-known petroleum process and is described in U.S. Pat. No. 3,951,781 to Owen (Mobil); U.S. Pat. No. 3,968,023 to Yan (Mobil); U.S. Pat. No. 3,972,807 to Uitti (UOP); U.S. Pat. No. 3,975,396 to Bushnell (Exxon); U.S. Pat. No. 3,981,797 to Kellar (UOP); U.S. Pat. No. 3,998,726 to Bunas (UOP); U.S. Pat. No. 4,017,383 to Beavon (Ralph M. Parsons); U.S. Pat. No. 4,054,512 to Dugan (Exxon); U.S. Pat. No. 4,101,415 to Crowley (Phillips); U.S. Pat. No. 4,125,458 to Bushnell (Exxon); and numerous others. Specific proprietary processes include the SOLVAHL solvent deasphalting process licensed by Institute Francais de Petrole, and the low-energy deasphalting process licensed by Foster Wheeler, U.S.A., shown schematically in FIG. 1. Deasphalting processes also include the ROSE supercritical fluid technology licensed by Kerr-McGee Corporation.
U.S. Pat. No. 5,601,697 to Miller et al. teaches SDA-produced asphalts (containing solvent deasphalting bottoms) made by blending SDA bottoms with aromatic extract and optionally, asphalt cement from vacuum bottoms, AC5. Preferably the extract is produced from an extraction process such as that employed in lubricating oil production. The blending process produces asphalts of superior characteristics, e.g., PG64-22, which can meet the new Strategic Highway Research Program (SHRP) specifications for dynamic sheer, creep stiffness, and direct tension (tensile strength). As the new SHRP asphalt specifications impact the marketplace, particularly aided by the recent increases in federal funds for highway construction and repair, these new asphalt products will be particularly advantageous.
Due to the aromatic nature of the lube plant extract used, there may exist applications in which the aromatic content should be reduced or eliminated from an environmental or toxicological standpoint. Also, there may be interruptions or reductions in the supply of the extract resulting from changes in the refinery operation. Accordingly, it would be advantageous to provide a less aromatic substitute for or additive to the aromatic extract which provides similar effects on solvent deasphalted bottoms-containing asphalts, namely, providing improved dynamic sheer, creep stiffness, and direct tension (tensile strength).
U.S. Pat. No. 4,381,992 to Wood et al. (Phillips) teaches the process for purification of used oil by removal of the ash forming components and then subjecting the material to vacuum fractionation. The patent discusses that such fractionation renders a bottoms material too heavy for use as a lubricating oil, but useful as a gear oil or as an asphalt additive. No further mention of usefulness of the bottoms material is made. The claims of the invention deal only with the purification of used oil processes, a method for fractionating the same and in no form discuss the novel findings of our invention.
U.S. Pat. No. 5,447,628 to Harrison, et al. teaches heating used lubricating oils to an additive decomposition temperature of 400.degree. F. (204.degree. C.) to 1000.degree. F. (538.degree. C.) via direct heat heat exchange by mixing with a heated product oil. The process provides a rerefined lube oil fraction free of organo-metallic compounds such as zinc dithiophosphate, and a bottoms fraction containing organo-metallics which can be used as an asphalt extender or fuel oil.
U.S. Pat. No. 4,101,414 to Kim, et al., incorporated herein by reference, discloses predistillation by steam stripping for several hours of a used lubricating oil stock in order to remove light oil, residual water, sulfur, and NO.sub.x. The temperature is kept at temperatures which avoid additive breakdown, and the process provides an odorless concentrate product upon vacuum distillation which contains heavy lube hydrocarbons, additives, metals, metal compounds, and the like. The concentrate product may be used as a grease, automotive undercoating, and a road sealant, inter alia.
German Patent DD 220,038-A1 discloses a binder for road building which comprises a propane bitumen, extract oil obtained in the selective refining of lubricating oil fractions, composed mainly of aromatic hydrocarbon fractions, and a deacidified, dehydrated and oil-freed cracking resin from controlled sulfuric acid refining of hydrocarbon oils and used oils. In contrast, the present invention does not utilize a resin fraction, but rather the heavy bottoms from distillation of used lubricant oils.